The stimulation of myocardial angiogenesis may be an important method to diminsh ischemia and improve the quality of patients' lives. Transmyocardial laser revascularization (TMR)is one such method that employs the use of a high powered laser to create a controlled injury and engender the natural angiogenic response. While clinical results with two different wavelengths of laser light are reportedly similar there are vast differences between the laser tissue interactions. We investigated whether this difference led to a myocardial functional change and whether the mechanisms whereby each laser achieves its clinical success is different.[unreadable] Employing a porcine model of chronic myocardial ischemia; cine MRI, hyperenhancement MRI, rest and stress echocardiography and histology were performed after TMR. There were significant improvements in myocardial function after treatment by a carbon dioxide that were not seen when a holmium:YAG device was used. Histology and MRI confirmed more scarrring and less angiogenesis with the Ho:YAG device at 6 weeks post treatment.